Conformation-dependent dynamic organic phosphorescence through thermal energy driven molecular rotations

Organic room-temperature phosphorescent (RTP) materials exhibiting reversible changes in optical properties upon exposure to external stimuli have shown great potential in diverse optoelectronic fields. Particularly, dynamic manipulation of response behaviors for such materials is of fundamental significance, but it remains a formidable challenge. Herein, a series of RTP polymers were prepared by incorporating phosphorescent rotors into polymer backbone, and these materials show color-tunable persistent luminescence upon excitation at different wavelengths. Experimental results and theoretical calculations revealed that the various molecular conformations of monomers are responsible for the excitation wavelength-dependent (Ex-De) RTP behavior. Impressively, after gaining insights into the underlying mechanism, dynamic control of Ex-De RTP behavior was achieved through thermal energy driven molecular rotations of monomers. Eventually, we demonstrate the practical applications of these amorphous polymers in anti-counterfeiting areas. These findings open new opportunities for the control of response behaviors of smart-responsive RTP materials through external stimuli rather than conventional covalent modification method.


Synthesis of P7 and P8:
The polymer was prepared by copolymerization of the M6 monomer (100 mg, 0.24 mmol, 1 eq) and acrylamide (872.23 mg, 12.28 mmol, 50 eq) by a radial polymerization with 2,2'-azobis(2methylpropionitrile) (AIBN) (40 mg) as radical initiator at 65°C under an argon atmosphere in DMF for 12 h. The resulting mixture was added into methanol to precipitate polymeric materials. Precipitation was repeatedly washed with methanol to give purified polymers. P7 polymer was prepared by using the same method. Supplementary Fig. 24 Synthesis. Synthetic route of C1.
Supplementary Fig. 37 The reversibility of phosphorescence peak between room temperature and high temperature. Ten cycles of phosphorescence wavelength variations measured at 30 ℃ and 120 ℃ (P1).
Supplementary Fig. 38 The delayed PL spectra of C1. a-e The delayed PL spectra of C1 at various excitation wavelengths (300-360 nm), upon heating from 30 ℃ to 120 ℃, f The delayed PL spectra of C1 upon heating from 30 ℃ to 120 ℃ under 300 nm excitation.  The method to calculate the fluorescence and phosphorescence quantum yields separately was performed according to previous literatures 1,2 . The phosphorescence bands could be obtained in their delayed emission spectrum. According to the structure of phosphorescence bands, the fluorescence and phosphorescence emission bands could be separated in steady state emission spectra. The ratio for fluorescence and phosphorescence quantum yields could be calculated with areas of separated fluorescence and phosphorescence bands. Thus, the fluorescence and phosphorescence quantum yields could be obtained by their total luminescence quantum yields and the ratio for the two relative quantum yields. The calculation method was added in the revised supplementary information.

Supplementary
Photoluminescence quantum efficiency was determined by using Edinburgh FLS980 spectrometer with the integrating sphere (142 mm in diameter) under ambient condition. The fluorescence and phosphorescence quantum efficiency (ΦF and ΦP) were calculated through the following formulas: where ΦE refers to the measured total emission quantum efficiency, AP and AE refer to the integral areas of phosphorescence and photoluminescence components in photoluminescence spectra, respectively.
Supplementary Fig. 55. Large area printing applications. Photographs of different animal cartoons printed on a A4 filter paper by using P3 as the ink before and after removing 300 nm and 365 nm irradiation.